Row_number() with distinct

Question

How to use row_number() with distinct ?
I want all the selected in distinct display but it only can display (a) table. How can i add more table in select row_number() ??
Here is my query.
SELECT
ROW_NUMBER() OVER (ORDER BY a.student_number) as No
FROM
SELECT DISTINCT
TO_CHAR(TO_DATE(c.study_intake, 'yyyymm'), upper('mon yyyy')) AS Study_intake,
     a.student_number,
     a.name,
     b.course_code,
     b.academic_semester,
     e.qualification,
     e.school,
     e.state,
     f.school_town,
     a.permanent_tel_no,
     a.mobile_no
FROM
     student_data a,
     student_course_master b,
     student_course_detail_subject c,
     student_qualification e,
     school_master f
WHERE
     a.student_number = b.student_number
AND b.student_key = c.student_key
AND e.student_key = a.student_key
AND b.student_course_status IN ('Completed','Active')
AND e.school = f.school_name(+)
AND e.state = f.state(+)      
)a

Answer 1

Did not get any help from them ;)
Regards,
Guru